The present invention relates to a ruthenium sputtering target and a ruthenium alloy sputtering target, and in particular relates to a sputtering target for forming a ruthenium oxide film for use as a lower electrode of a ferroelectric capacitor of a semiconductor memory.
In recent years, ruthenium or ruthenium alloy is being used as an electronics material such as a ferroelectric capacitor for use in a semiconductor memory. Generally, the sputtering method is often used for forming a ruthenium thin film. While the sputtering method itself is a well-known method in the field of electronics, demanded is a target made from ruthenium or ruthenium alloy comprising uniform and stable characteristics that are suitable for sputtering.
Generally speaking, a commercially available ruthenium material having a relatively high purity is a 3N level powder, but materials recently used in the field of electronics are demanded of even higher purification as disclosed in the following Patent Documents from the perspective of preventing the generation of noise and improving characteristics, and a 5N purity level is now required as a high purity ruthenium sputtering target.
For example, Patent Document 1 describes a high purity ruthenium target wherein alkali metal elements are each less than 1 ppm, alkali earth metal elements are each less than 1 ppm, transition metal elements are each less than 1 ppm, radioactive elements are each less than 10 ppb, carbon and gas components (oxygen, hydrogen, nitrogen, and chlorine) are less than 500 ppm in total, and purity of ruthenium excluding gas component elements is 99.995% or more.
Patent Document 2 describes a high purity ruthenium target wherein content of alkali metal elements is each 0.1 wtppm or less, content of alkali earth metal elements is each 0.1 wtppm or less, content of transition metal elements other than a platinum group element is each 0.1 wtppm or less, content of radioactive isotope elements is each 1 wtppb or less, total content of gas component elements is 30 wtppm or less, and purity is 99.995 wt % or more. Moreover, Patent Document 3 describes a high purity ruthenium target containing 10 wtppm or less of oxygen, 10 wtppm or less of nitrogen, and having a purity of 5N level or higher. In addition, Patent Document 4 describes a sputtering target of a composition containing 1 to 9 ppm of Si, and the remainder being Ru having a purity 99.998% or higher.
Nevertheless, when a ruthenium material is highly purified for use in a sputtering target, it is known that crystal growth is promoted and coarse crystal grains are formed (for example, Patent Document 5). When these coarse crystal grains exist in the sputtering target, there is a problem in that they promote an abnormal discharge (arcing) during sputtering, and thereby increase the generation of particles and deteriorate the yield of products.